As the third anniversary of the Deepwater Horizon oil spill approaches on April 20th it is important to look at the lessons learned as well as the current state of offshore drilling. The Deepwater Horizon spill released over four million barrels of oil into the Gulf of Mexico before finally being capped after 84 days (Camilli et al. 2010, Crone and Tolstoy 2010) .

According to the United States Fish and Wildlife Service’s 2010 report 491,292 pounds of oiled debris were removed from environmentally sensitive areas in Florida alone. It is also estimated that the spill resulted in a total economic loss of $12.48 billion as a result of damages to commercial fishing, tourism, and coastal real estate values (Smith, Jr. et al. 2010).

However, it is not just catastrophic accidents like this one that can damage the marine environment. There are risks associated with everyday tasks on an oilrig (Menzie 1982, Holdway 2002). There is even risk of harm to the marine environment during the exploration phase if seismic airguns are used (Popper et al. 2005, Lucke et al. 2009, Oceana 2012).

During exploration for oil and gas formations seismic airguns are towed with a vessel and release pulses of sounds from 225 to 250 decibels several times per minute (Richardson et al. 1995). To put that number in perspective, the noise from a jet engine is 140 decibels—seismic airguns are 100,000 times more intense than a jet engine. Airguns produce sound by creating a compressed air bubble, which collapses under the pressure of the water (Popper et al. 2005).

The sound then reflects off geologic formations and is measured by hydrophone arrays towed behind a ship. The time it takes for sound to bounce back indicates the presence of oil and gas (Figure 2). These studies are often conducted continuously over the course of several weeks. According to Lucke et al. (2009), seismic surveys are one of the largest contributors to noise budgets in most of the world’s oceans.

Image courtesy Oceana

With the extremely intense sounds being produced it comes as no surprise that marine mammals and fishes can experience a wide range of potential effects. These include: immediate death, damage to body tissue, temporary or permanent hearing loss, and changes in behavior (Popper et al. 2005).

Currently, the United States Department of the Interior (DOI) has a proposal allowing seismic airgun testing for oil and gas exploration in the Atlantic Ocean from Delaware to Florida. According to their Draft Environmental Impact Statement at least 138,500 whale and dolphin injuries will occur, including nine critically endangered North Atlantic right whales (Eubalaena glacialis) (U.S. DOI 2012) (Figure 3). In addition, the high intensity sound may displace important commercial fish, putting 200,000 East Coast fishing jobs in jeopardy (Oceana 2012).

It is clear that seismic airgun use cause harm to the marine environment, but this has often been a trade-off for great economic gains. In this case, no such gains are expected. Seismic airgun testing does not create any permanent jobs in Florida and offshore oil and gas lease sales are not scheduled to occur until 2017 at the earliest. Oil or gas installations would not begin production until 2025-2030 if lease sales do occur (Oceana 2012). By that time, I hope the United States will be leading the way with renewable energy rather than desperately exploiting a dwindling resource whose consumption drives global climate change.

Menzie, C.A. The environmental implications of offshore oil and gas activities an overview of the effects associated with routine discharges based on the American experience. Environmental Science and Technology 16: 454-472 (1982).

It is inappropriate and misleading to contrast airgun (source) levels of 225 to 250 dB with jet engine noise at 140 dB with no reference to the different dB scales in water vs. air, and the greatly different densities and impedances of the two media. The related statement that [noise from] airguns is 100,000 times more intense than that from a jet engine is even more inappropriate. There are legitimate concerns about the biological effects of airguns, but the discussion is not helped by such misleading statements.

Thank you for your criticism and you are right I should have mentioned something about the difference between air and water. However, I chose to use the jet engine comparison since it is a land-based example to which people can easily relate. I suppose a more appropriate comparison would be to say seismic airgun discharges on land register at 190dB–a number still 5,000 times more intense than the 140 dB emitted by a jet engine.